More Pitfalls From Purported Exit Polls

Published numbers supposedly leaked from exit polls appear to have missed the mark yet again.

The Drudge Report, the popular political gossip site, published the headline “Obama Large in Exit Polls” at 6:40 ET. A few minutes later, that changed to “Obama Large in Some Exit Polls.” That was followed by numbers for nine states, purportedly leaked from the consortium that conducts exit polls for the media, and all showing Sen. Barack Obama in the lead. A few minutes later, those were joined by states where Sen. Hillary Clinton was leading, and by the caveat, “WARNING: EXIT NUMBERS EARLY AND DO NOT REPRESENT ACTUAL VOTES.”

Within a couple of hours, those numbers were gone from Drudge’s front page, but they’d been picked up by some otherblogs. Meanwhile, similar numbers showed up on severalU.K.newspapers. These typically came with disclaimers; for instance, the Guardian’s writer sarcastically headlined the numbers, “Scientifically accurate exit polls!!!”

And for good reason: The purportedly leaked data showed Mr. Obama with a narrow lead in Massachussets and a six-point lead in New Jersey, both states that Mrs. Clinton was projected to have won by 10 p.m. ET.

In 2000 and 2004, early exit-poll numbers for the general election mistakenly suggested a Democratic presidential candidate had won — and in 2004, those numbers reached the Web by early afternoon. (In a sign of changing times, a Wall Street Journal article in 2004 about the numbers referred to their publication by “the Web-log operators called bloggers.”) Starting in 2006, the exit-polling media consortium imposed a quarantine — no cellphones nor Blackberrys allowed in the exit-poll tallying room — to ensure no numbers leak early.

The published exit-poll numbers this time around may have been preliminary, or fabricated, but even if they weren’t, it wouldn’t be a surprise if by themselves they missed the mark. As Pollster.com’s Mark Blumenthal explains, exit polls are used by the news media as one tool in a projection arsenal that also includes pre-election polls and, most importantly, actual vote returns. The numbers are useful, he writes, but exclude absentee ballots, and are typically based on small sample sizes.

Proper projections don’t just incorporate exit polls and state-level vote counts, but drill down to the precinct level. That’s because trailing candidates may be leading in areas where the counting lags. For instance, with 62% of Missouri precincts having reported results by 10:40 p.m., Mrs. Clinton was leading Mr. Obama, 53% to 44%. But in Obama-leaning counties that include St. Louis and Kansas City, fewer than 50% of precincts had reported. Thus the state remained too close to call. Those published “exit polls”? They showed Mr. Obama winning.

Further reading: Exit-poll numbers aren’t used only to declare winners. Here’s a roundup of what exiting voters told pollsters topped their list of concerns.

About The Numbers

The Wall Street Journal examines numbers in the news, business and politics. Some numbers are flat-out wrong or biased, while others are valid and help us make informed decisions. We tell the stories behind the stats in occasional updates on this blog.